I. Field of the Invention
The present invention relates to bridging structures for use between joists or other similar construction elements. More particularly, the present invention relates to flexible bridging, such as strapping, that can be applied with a selectively adjustable tension and/or length between adjacent joists.
II. Prior Art Statement
Bridging is commonly used between floor joists, roof rafters, beams, trusses, framing studs and similar construction elements to increase the strength and stability of those elements. However, the advantages of bridging can be best explained when applied to a floor joist construction.
The use of bridging between joists in a floor construction increases the load bearing capacity of the floor. Bridging mechanically joins the various floor joists together. As such, bridging restrains the independent movement of any single joist. Bridging therefore helps keep the various joists straight and parallel to one another. Restraining joists from twisting along the line of bridging increases the strength and stiffness of individual joists. When individual joists are loaded without bridging, the individual joists may bend and twist under the load and move away from their desired vertical orientation. As a result, the load bearing capacity of the twisted joist is greatly reduced. Bridging joins joists together in a manner that limits the amount of twisting each joist can experience. Bridging also acts to spread a concentrated load positioned atop a single joist among the surrounding joists. Consequently, bridging increases the static stiffness and strength of the floor. In view of the increase in structural strength and stiffness created by bridging, the load bearing capacity manufactured into individual joists can be reduced, thereby enabling joists to be manufactured with both a material and labor savings.
Although floors are designed with static strength and deflection constraints, the floor's dynamic performance often determines the perceived quality of the overall construction. Floors which never fail due to strength or static deflections may not prevent annoying vibrations from arising due to the dynamic loads of occupants in motion.
The availability of higher strength materials has reduced the weight and size of structural members and have made floor systems more sensitive to vibrations. Costly measures are commonly taken to reduce occupant induced floor vibrations. For instance, oversized joists are often selected. Alternatively, the floor deck is often glued to increase composite action between the deck and joists. The cost of these construction practices add to both the labor and costs of installing the flooring.
Increasing floor stiffness transverse to the direction of the joist span is advantageous in that it provides a more efficient means of reducing vibration than does increasing floor stiffness in the direction of the joist span. This is because the vibrational mode shapes develop transverse to the joist span in the direction of the bridging line.
Effective bridging efficiently increases floor stiffness transverse to the joist span and restrains rotation of the joist. These effects raise the fundamental frequency of the floor and separate closely spaced frequency modes which can interact to amplify vibrational amplitudes.
One type of conventional bridging often used in residential construction comprises two pieces of lumber installed between adjacent joists in an X-shaped pattern. Each piece of lumber is then nailed at its upper and lower ends between each joist. A similar type of conventional bridging utilizes pieces of lumber cut to the correct length to fit between adjacent joists with respect to the center-to-center joist spacing. Each end of the lumber is then nailed directly to the joist it contacts. Both bridging types require lumber to be cut to size and nailed to the joists. As such, lumber-based bridging is highly time consuming and labor intensive.
In an attempt to reduce the time and labor involved with lumber based bridging, prefabricated steel bridging devices have been widely developed throughout the prior art. The simplest form of this prefabricated metal bridging is comprised of two metal brackets. Each metal bracket is then directly nailed to the vertical walls of adjacent joists to form an overall X-shaped configuration. Such prior art bridging devices are exemplified in U.S. Pat. No. 459,900 to Moore, entitled BRIDGING FOR FLOORING JOISTS; U.S. Pat. No. 682,086 to Kearney, entitled CROSS BRIDGE; U.S. Pat. No. 918,949 to Bertram, entitled JOIST BRIDGING; U.S. Pat. No. 3,018,522 to Reidelbach, entitled METAL BRIDGING FOR JOISTS; and U.S. Pat. No. 2,803,045 to Horner, entitled JOIST BRACE. A similar type of prior art metal bridging also utilizes two metal brackets nailed between joists in an X-shaped configuration. However, the ends of each bracket are nailed to the top and bottom horizontal surfaces of the joists, rather than to the vertical sides of the joists. Such prior art bridging is exemplified by U.S. Pat. No. 2,565,875 to Musacchia, entitled RIBBED METAL CROSS BRIDGING; U.S. Pat. No. 2,455,904 to Meulenbergh, entitled METAL CROSS BRIDGING; and U.S. Pat. No. 1,685,729 to Stone, entitled BRIDGING CONSTRUCTION FOR JOISTS.
The strength, rigidity and method of installment of the above described lumber-based and metal bridging are problematic. The relatively large cross sectional stiffness and configuration of these prior art bridging types result in high loads on connections. The relatively large stiffness of prior art bridging in relation to that of the joist span results in heavy loads being carried by the bridging. In such prior art bridging, the strength of the bridging is dependent upon the size and number of nails used to secure the bridging to the joists. As such, the strength of the bridging can be no greater than the forces retaining the anchoring nails within the joists. Prior art bridging which terminates at its connection to the joist must transfer all loads in the bridging element to the joist. In many load cases, bridging elements connected to both sides of the joist's top or bottom edge are loaded in tension. If the bridging element were continuous over the joist edge, only the difference in horizontal components of the bridging's tension forces are transferred to the joist on either side of the joist. Therefore, the connections of prior art bridging which terminates at the joist are subjected to much higher loads than bridging which is continuous over the joist. As a result, connections of bridging terminating at the joist are severely overloaded, resulting in a loss of connection rigidity. Moreover, the overloaded nails are prone to squeaking. Repairs for floor squeaking are troublesome and costly. Furthermore, prior art cross bridging which terminates at the joist requires twice the number of connections as bridging which is continuous over the joist. One connection of continuous bridging simultaneously attaches two bridging elements to the joist.
Prefabricated metal bridging has further disadvantages in that the bridging is prone to improper installation methods that adversely affects the rigidity of the bridging. Certain prior art metal bridging devices require that the bridging be bent to the angle of the joist prior to being nailed to the joist. Sharply bending the metal bridging at the proper position by hand is problematic. Some prior art metal bridging is manufactured with prefabricated holes through which the nails can be driven. Commonly, such metal bridging bends at the points of the nail holes rather than at the proper point of flexure. As a result, the bends that occur in such metal bridging are seldom at the proper location. The bridging must bend at the proper points of flexure and straighten out any kinks before the bridging can transfer significant loads between joists. Consequently, the misplaced bend causes points of slack in the bridging that lessen the rigidity, and consequently the effectiveness of the bridging.
Prefabricated metal bridging that attaches to the horizontal surfaces of joists is particularly difficult to install. For each bridging bracket, the upper end of the bracket must be nailed before the floor decking is installed. This may require a hazardous balancing act while working from the top of the suspended joists. Working overhead while standing on a raised work surface makes connecting the bridging to the underside of a joist difficult. Moreover, fastening the bridging requires one hand to hold the nail; the other hand to hold the hammer; and the mythical third hand to properly position the bridging. Furthermore, when installing such bridging on joists, workmen may nail the bridging bracket too close to the edge of the joist or fail to drive the specified amount of nails through the bridging into the joist. If such mistakes occur, the strength of the bridging design is greatly undermined. Furthermore, variations in the joist spacing and depth cannot be easily compensated for by the prefabricated bridging. Nail holes are provided only at certain locations on some metal bridging, as is exemplified by U.S. Pat. No. 1,523,711 to Powell, entitled BUILDERS HARDWARE STRIPS WITH MULTIPLE HOLES. When such prior art bridging is installed, one end of the bridging is nailed down first. consequently, it is possible for the other end of the bridging to misalign with the joist edge and therefore the nail holes, present in the bridging, may not align over the center of the joist. If the nails are attached too close to the edge of the joist, the joist may splinter and the bridging may detach as the bridging and the floor joists are repeatedly stressed. It can therefore be seen that with certain prior art devices, small variations in the position of the joists may create an inferior bridging installation.
In an attempt to solve the problems of nailing and fit that are prevalent with static prefabricated metal bridging, adjustable bridging has been developed in the prior art. In such adjustable bridging, the lengths of the various bridging members can be selectively adjusted. consequently, the bridging can be properly installed despite small variations that may exist among the joists. Such prior art bridging devices are exemplified by U.S. Pat. No. 3,102,306 to Hutchinson, entitled METHOD OF MANUFACTURING BRACING; U.S. Pat. No. 1,496,133 to Rothrock, entitled ADJUSTABLE WOOD CROSS BRIDGING FOR FLOORS AND JOISTS; U.S. Pat. No. 2,623,246 to Pestak, entitled BRIDGING FOR FLOOR JOISTS and U.S. Pat. No. 3,077,009 to Taber, entitled BRACING. The problem with such bridging is that it requires telescoping members, or other various complicated slide adjustments that are expensive to manufacture. Consequently, the cost of such bridging is expensive as compared to other conventional bridging.
In view of the prior art in bridging for joists, there exists a need for a bridging device that is adjustable in its application, simple to install rigidly, can be connected to joists before the joists are installed, is inexpensive to manufacture, is continuous over the joists to reduce loads on connections and the number of connections and does not rely on hand driven nails as the sole means of providing connection rigidity. All these criteria are provided for by the present invention herein described.